The present disclosure generally relates to a laser communication system, and specifically relates to an optical transceiver for controlling a steering angle between a receive light beam and a transmit light beam.
Laser-based systems, such as laser communication systems, commonly employ multiple laser beams. A bidirectional laser communication system (e.g., in space settings) can include two or more laser terminals (e.g., either stationary or non-stationary terminals) that communicate between each other by encoding information into light beams. To exchange information data between two laser terminals of the laser communication system, each laser terminal transmits a light beam with encoded data to another laser terminal and receives another light beam with encoded data transmitted from the other laser terminal.
If a relative velocity between the laser terminals is low (e.g., below a threshold velocity), the light beam transmitted from the laser terminal and other light beam received from the other light terminal are substantially aligned along the same line of sight (LOS). On the other hand, if the relative velocity between the laser terminals is above the threshold velocity (which often happens in ground-space and space-to-space terminal communications), the relativistic effect needs to be accounted for when the laser terminals communicate between each other. Therefore, for accurate communication between the laser terminals, it is required to differentiate between a position of the other laser terminal relative to the laser terminal when a light beam is received from the other light terminal and another future position of the other laser terminal relative to the laser terminal for directing another light beam toward the other light terminal. Typically, the light beam received from the other laser terminal and the other light beam transmitted to the other light terminal are not parallel to each other. Instead, from the perspective of the laser terminal, there is a certain differential (point-ahead) angle between transmit and receive light beams.
The conventional approach is to implement two very precise separate pointing systems at the laser terminal. A first pointing system (e.g., receiving pointing system) is required to direct the receive light beam toward a detector of the laser terminal. A second pointing system (e.g., transmitting pointing system) implemented separately from the first pointing system needs to be configured to provide a differential (point-ahead) angle to send the transmit light beam to the other laser terminal accounting for a relative velocity and separation between the laser terminals. Accordingly, the conventional approach is relatively complex, as it uses two separate pointing systems to accurately align transmit and receive light beams that must be precisely aligned to each other.